1. Field of the Invention
The present invention relates to an organic light emitting device, and more particularly, to an organic light emitting diode (OLED) that can prevent a sealing material from overflowing and affecting normal operation of the OLED.
2. Description of the Prior Art
In various types of flat panel displays, since an OLED has many beneficial characteristics, such as having a spontaneous light source, a wide viewing angle, high response velocity, full-color, simpler structure, and a wide operating temperature, and saving power, the OLED has been used extensively in small and medium scale portable display fields.
Please refer to FIG. 1, which is a cross-sectional view of a conventional OLED 10. As shown in FIG. 1, the conventional OLED 10 mainly includes a transparent glass substrate 12, a transparent conductive layer 14 positioned on the glass substrate 10, an organic layer 16 positioned on a predetermined region of the transparent conductive layer 14, and a metal layer 18 positioned on the organic layer 16. The transparent conductive layer 14 is used as an anode of the OLED 10, and the metal layer 18 is used as a cathode of the OLED 10.
In addition, the organic layer 16 further includes a hole transport layer (HTL) 20, an emitting layer (EML) 22, and an electron transport layer (ETL) 24 Positioned on the transparent conductive layer 14, respectively. Furthermore, a hole injection layer (HIL, not show in FIG. 1) can be positioned between the transparent conductive layer 14 and the HTL 20, and an electron injection layer (EIL, not shown in FIG. 1) can be formed between the metal layer 18 and the ETL 24, for improving an adhesion problem of the transparent conductive layer 14, the organic layer 16, and the metal layer 18, and benefiting electrons and holes being injected into the organic layer 16. Moreover, another emitting layer (not shown in FIG. 1) that has an ability of transporting the electrons, or another HTL (not shown in FIG. 1) that has an ability of irradiating light, can be chosen to simply structure of the OLED. Typically, the transparent conductive layer 14 is composed of indium tin oxide (ITO) or indium zinc oxide (IZO). The organic layer 16 is formed by utilizing a thermal evaporation process, the HTL 20 is composed of diamine chemical Compound, and the metal layer 18 is composed of magnesium (Mg), aluminum (Al), lithium (Li) or an alloy of Mg, Al, and Li.
When a direct current (DC) voltage is applied to the OLED 10, the electrons penetrate through the ETL 24 from the metal layer 18 (the cathode of the OLED 10), and the holes penetrate through the HTL 20 from the transparent conductive layer 14 (the anode of the OLED 10), and then the electrons and the holes are both injected into the emitting layer 22. Further, the electrons and the holes move and re-combine together to form an electron/hole pair in the emitting layer 22, and organic light emitting molecules of the emitting layer 22 are excited to an excitation state due to a potential difference caused by an external electric field. When the molecules discharge energy and return to a base sate, a fixed ratio of the discharging energy (i.e. the quantum efficiency, QE) is liberated in photon. Thereafter, the photon permeates the glass substrate 12 and illuminates downward. This is caused by electroluminescence of the OLED 10.
However, the organic layer 16 and the metal layer 18 of the OLED 10 are very sensitive to moisture and oxygen gas. As soon as the organic layer 16 and the metal layer 18 are in touch with moisture and oxygen gas, the organic layer 16 could peel off the transparent conductive layer 14 and the metal layer 18, the metal layer 18 could be oxidized, and dark spots could be generated in the OLED, reducing display quality, lowering glow of the OLED, and decreasing life of the OLED. Therefore, a passivation and encapsulation material of the OLED must have characteristics of perfect anti-abrasiveness, high thermal conductivity, and lower moisture permeability, to prevent the organic layer from contacting with the outside environment efficiently, and to increase the life of the OLED.
Please refer to FIG. 1 again, an encapsulation process of the conventional OLED 10 utilizes a sealing material 26, such as a binder composed of high polymer glue materials, to bind a container 28 made of glass or metal on the glass substrate 12. Then, dry nitrogen gas is injected into a hollow part between the container 28 and the glass substrate 12 to accomplish the encapsulation process of the OLED 10. In addition, a desiccating agent (not shown in FIG. 1) can be positioned in the OLED 10 for adsorbing moisture that permeates from outside into the OLED 10 caused by imperfect encapsulation of the OLED 10, and preventing the organic layer 16 of the OLED 10 from moistening.
The conventional container 28 provides good isolation with the OLED 10, moisture and oxygen gas. However, quantity of the sealing material 26 has to be properly measured during a lamination process of the encapsulation process. If an excess of the sealing material 26 is used for a better airtightness of the OLED 10, the sealing material 26 could overflow into an inside of the OLED, due to improper distribution of the sealing material or unbalanced pressure during the lamination process. Therefore, the excess sealing materials are in touch with the organic layer 16 and affect the normal operation of the OLED 10. Consequently, the conventional encapsulation process of the OLED always decreases the quality of the sealing material to prevent the above-mentioned problem. On the other hand, if an insufficient amount of sealing material 26 is used to bind the glass substrate 12 and the container 28, the container 28 would not be sealed up with the glass substrate 12 closely, moisture and oxygen gas easily permeate the OLED 10, and the container 28 is easily peeled off the glass substrate 12. In addition, in order to increase the adhesion of the container 28 and the glass substrate 12, a surface of the conventional container 28 that correspond to the glass substrate 12 can be sandblasted or etched to be a rough surface for raising adhesive area of the container 28 and the glass substrate 12. However, illumination quality of the OLED is affected, and the container 28 with a rough surface cannot be applied in a top emission OLED (TOLED) display.
It is therefore a primary objective of the claimed invention to provide an organic light emitting device to avoid the above-mentioned problems.
According to the preferred embodiment of the claimed invention, an organic light emitting diode (OLED) is introduced. The OLED comprises a bottom substrate including a bottom electrode positioned on an upper surface of the bottom substrate, an organic layer positioned on a predetermined region of the bottom electrode, a top electrode positioned on the organic layer, and a spot glue region positioned on the bottom substrate and outside the predetermined region of the bottom electrode, a top substrate positioned parallel with the bottom substrate, and a lower surface of the top substrate having at least one first ditch formed within the top substrate, and a sealing material positioned on the spot glue region of the bottom substrate for binding the top substrate and the bottom substrate together. The first ditch is used to prevent the sealing material from overflowing into the predetermined region of the bottom substrate and affecting normal operation of the OLED.
Since the OLED of the claimed invention has the ditches positioned within the top substrate of the OLED, an excess sealing material can flow into the ditches if an excess of the sealing material is utilized to bind the top substrate and the bottom substrate together. Therefore, the excess sealing material does not contact with the organic layer of the OLED and affect the normal operation of the OLED.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.